(Vol. v., p. 370.)
Your Querist J. C. E. is informed that the singular phenomenon of the
formation of ice in the beds of running rivers has not escaped the notice
of scientific observers. M. Arago has devoted a paper to its investigation
in the _Annuaire du Bureau des Longitudes_ for 1832 or 1833, in which he
specifies the rivers in which it has been observed. Indeed, although from
its nature it is likely to escape notice, it is probably of not infrequent
occurrence. Ireland, in his _Picturesque Views of the Thames_, quoting Dr.
Plot, speaks of the subaqueous ice of that river. Colonel Jackson, in the
fifth volume of the _Journal of the Royal Geographical Society_, alludes to
its formation in the Neva, in a paper on the congelation of that river; and
in the following volume of the same Journal is an article by Mr. Weitz,
especially devoted to the ground ice of the rivers of Siberia. More
recently, Mr. Eisdale has contributed the result of his researches upon the
same subject to the _Edinburgh New Philosophical Journal_, vol. xvii.; and,
finally, Dr. Farquharson has made public his observations upon the
ground-gru of the rivers Don and Leochal, in Lincolnshire, in the
_Philosophical Transactions_ for 1835. There is also an article on the
subject in one of the later volumes of the _Penny_ or _Saturday_ Magazines.
That bodies of running, water, the surface of which solidifies when exposed
to a diminished temperature, should have a tendency to congelate in their
sheltered depths, seems an anomaly which demands inquiry and explanation;
and accordingly each of the above-mentioned writers has raised an
hypothesis more or less probable, to account for the phenomenon. Dr.
Farquharson would attribute it to the radiation of heat from the bottom, as
dew is formed by radiation from the surface of the earth; but a
consideration of the supervening obstacles to radiation--a body of moving
water thickly coated with ice and even snow--destroys the plausibility of
his theory. That of Mr. Eisdale, that the frozen _spiculæ_ of the
atmosphere falling into the water become _nuclei_, around which the water
at the bottom freezes, seems merely frivolous. The explanation of M. Arago
is more satisfactory, viz. that the lower currents of water being less
rapid in motion than those intermediate, or at the surface, congelation may
be expected at a lower temperature (say 32° Fahr.), the process of
crystallisation being favoured by the pebbles, fragments of wood, and the
uneven surface of the river's bed. After all, however, the phenomenon has
been but imperfectly investigated under its various manifestations, and its
real cause probably remains yet to be discovered.